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Abstract

Two novel classes of spherical invisibility cloaks based on nonlinear transformation have been studied. The cloaking characteristics are presented by segmenting the nonlinear transformation based spherical cloak into concentric isotropic homogeneous coatings. Detailed investigations of the optimal discretization (e.g., thickness control of each layer, nonlinear factor, etc.) are presented for both linear and nonlinear spherical cloaks and their effects on invisibility performance are also discussed. The cloaking properties and our choice of optimal segmentation are verified by the numerical simulation of not only near-field electric-field distribution but also the far-field radar cross section (RCS).

Figures (8)

The discretization of a general anisotropic spherical cloak (a) into an equivalent isotropic coated structure (b). An illustrative example for the conversion from the n-th anisotropic initial-layer (width is rn−rn−1) into its two sub-layers (isotropic) with equal thickness (rn−rn−1)=2 has been shown.

The concave-down nonlinear transformation. When x<0.1, all mapping curves are overlapping, meaning they effectively lead to the same performance. When x becomes large, the curve will nearly become a step function over 1λ<r<2λ.

Near-field interaction in the presence of the proposed nonlinear spherical cloak with different values of x for the concave-down class. The inner region 0<r<R1 is filled by PEC. M is set to be 40. Frequency is 2GHz. The total electric fields are plotted only in the region r>R2 in (e–h).

The concave-up nonlinear transformation. When x=1, it is exactly Pendry’s linear cloak, which can be verified by inserting x=1 into Eq. (12). When x gets extremely large, the mapping curve will nearly become a sharp impulse when r→2λ.

Re[Etotal] on x-z plane for the proposed concave-up nonlinear transformation cloaks at x=1, x=4 and x=10, respectively. Figs. 7(a–c) present total electric fields in all areas while Figs. 7(e–f) show the total fields only outside the cloak (r>R2). M=40 and f=2GHz. In order to show the disturbance in surrounding outer space, the plot range is larger (from -0.6m to 0.6m) in the right column.